The present invention relates to a fuel cell system and a fuel cell system failure judgment method, and more particularly to an improved technology for use in performing failure detection and judgment in a reaction gas passage accurately in a short time.
As a power generating system for a fuel cell hybrid vehicle, there has been used a fuel cell system capable of directly deriving chemical energy, which has been generated by a redox reaction of reaction gas (fuel gas or oxidant gas), as electric energy. In this type of fuel cell system, various shut-off valves (for example, a high-pressure hydrogen tank valve, a hydrogen supply valve, an FC inlet valve, an FC outlet valve, a purge valve, and the like) are arranged in a fuel gas supply passage for use in supplying fuel gas from a hydrogen supply source to a fuel cell.
As a failure diagnosis technique for these various shut-off valves, for example, Japanese Patent Laid-Open No. 2000-274311 has suggested a technology of creating a closed space in a fuel gas supply passage of a vehicle by closing a shut-off valve arranged in the fuel gas supply passage and determining a valve failure when a pressure drop rate of the closed space with respect to elapsed time is lower than a pressure drop rate threshold.
The pressure drop rate in the downstream of the shut-off valve varies according to a driving condition of the vehicle, namely a fuel consumption rate. Therefore, where the fuel consumption rate decreases according to the vehicle driving condition, a lot of time is required to reduce the pressure in the downstream of the shut-off valve, which inhibits rapid failure diagnosis.
In view of the above background of the invention, Japanese Patent Laid-Open No. 2003-308868 has suggested a technology of increasing a fuel consumption rate to reduce the pressure in the downstream of a shut-off valve in a short time by increasing the electric power consumption of auxiliary devices mounted on a vehicle when performing a failure diagnosis of the shut-off valve. Furthermore, it has disclosed that a combustion chamber is used to consume the fuel if the fuel consumption is insufficient only with the electric power consumption of the auxiliary devices.    [Patent Document 1] Japanese Patent Laid-Open No. 2000-274311    [Patent Document 2] Japanese Patent Laid-Open No. 2003-308868